The invention relates to an electric incandescent lamp comprising
a blown glass lamp vessel or envelope sealed in a vacuum-tight manner having PA0 an axis of symmetry and PA0 a largest diameter transverse to the axis of symmetry. PA0 lamps such as those described in the above-cited U.S. Pat. No. 2,110,590, having a mirror-coated parabolically curved wall portion opposite to which a window is located. The window is glazed (is slightly light-scattering) for example due to an etching treatment and/or is colored; PA0 lamps having a substantially spherical lamp bulb which is transparent or is frosted or which is coated with a white or colored light-scattering layer; PA0 lamps having a conical wall portion adjacent to, and a curved wall portion opposite to the neck-shaped wall portion, the conical wall portion being provided with a white or colored light-scattering layer and the curved wall portion being slightly light-scattering and, as the case may be, being colored. These lamps emit light on all sides, but supply along the axis is directions opposite the neck-shaped wall portion a higher luminous intensity than in other directions; and PA0 lamps having opposite to the neck-shaped wall portion a spherical wall portion which is mirror-coated or is provided, for example with a white light-scattering coating.
A neck-shaped first wall portion is behind the largest diameter and has a free end carrying a lamp cap having electric contacts. The lamp vessel has an internally concave second wall portion and an internally concave third wall portion. An internally concave fouth wall portion is located opposite the lamp cap in front of the largest diameter. A helically wound filament is supported about the axis of symmetry substantially in a transverse plane. Current supply conductors interconnect the filament and contacts on the lamp cap. The invention also relates to a blown glass bulb suitable for use in the lamp.
A lamp of this type is known from U.S. Pat. No. 2,110,590.
In the known lamp the second wall portion together with a reflector arranged within the neck-shaped wall portion constitutes half an ellipse when viewed in axial cross-section. The third wall portion is a branch of a parabola which is revolved about an axis parallel to the parabola axis, with the parabola axis being located between the branch of the parabola and the axis of revolution. The two wall portions are mirror coated and their foci are located on a circle. The filament is arranged in the plane through these foci.
The known lamp provides a solution to the problem of parabolic reflectors being too narrow in the focal plane if the filament is to be mounted in a deep reflector so as to obtain a satisfactory beam of generated light and avoids the transverse dimensions of the lamp exceeding a conventional size.
As in the known lamp the branches of the parabola are moved apart in an axial cross-section so that the lamp vessel in the focal plane is wider. Yet the filament in the focal plane is located in a narrow portion of the lamp vessel, remote from the largest diameter of the lamp vessel. A drawback of the known lamp therefore is that only filaments consuming a relatively low power can be mounted in the lamp vessel in order to avoid overheating of the lamp vessel.
Electric lamps having a power value between 15 and 100 W, for example 15, 25, 40, 60, 75 and 100 W intended to be operated at a standard voltage are manufactured in a large number of types. The finish, the coating and the processing of the lamp vessel wall, and also its shape and the size and shape of the inner parts of the lamp are different.
The electric incandescent lamps for operation at the mains voltage in the said power range include:
The manufacture of this large number of lamp types is very complicated due to the variety of lamp vessel types which require on and between the production machinery their own supply and lead-out mechanisms and their own transport means, and which moreover require individual packaging. The readjustment of production machines from one lamp type to the other is thus a very laborious operation. Another complication of their manufacture is that the various types of lamps require their own means to keep the filament positioned.